Writing a one-time scrapbook service in Python

Some people need to convey small messages. But how to do this if you use various social networks and instant messengers, in the safety of data transfer through which you doubt.

Some people use the services of self-destructing encrypted notes for this. But here the question arises whether these services can be trusted and whether they really destroy notes after reading them.

Python cryptography Flask Heroku.

github
Heroku

Virtualenv.

virtualenv

pip install virtualenv

mkdir encnotes
cd encnotes
virtualenv venv
source venv/bin/activate ( nix )
venv\Scripts\activate ( Windows )

requirements.txt :

cryptography
Flask
Flask-Migrate
Flask-SQLAlchemy
Flask-WTF
Flask-Bootstrap
Flask-SSLify

pip , requirements.txt

pip install -r requirements.txt

encnotes.py. . . .

import os
import random
from cryptography.fernet import Fernet
from flask import Flask, render_template, url_for
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate
from flask_wtf import FlaskForm
from flask_bootstrap import Bootstrap
from flask_sslify import SSLify
from wtforms import TextAreaField, SubmitField
from wtforms.validators import DataRequired, Length

,

class Config():
    SECRET_KEY = os.environ.get('SECRET_KEY')
    SQLALCHEMY_TRACK_MODIFICATIONS = False
    SQLALCHEMY_DATABASE_URI = os.environ.get('DATABASE_URL')
    SITE_URL = 'https://encnote.herokuapp.com'

SECRET_KEY — . , , . Flask-WTF Cross-Site Request Forgery CSRF.

SQLALCHEMY_TRACK_MODIFICATIONS — ,
, .

SITE_URL — , Heroku.

Flask Config

app = Flask(__name__)
app.config.from_object(Config)
db = SQLAlchemy(app)
migrate = Migrate(app, db)
bootstrap = Bootstrap(app)
sslify = SSLify(app)

, . 3 :

• id — ,
• number — , .
  1000000 9999999
• ciptext —

.

class Note(db.Model):
    __tablename__ = 'notes'
    id = db.Column(db.Integer, primary_key=True)
    number = db.Column(db.Integer, unique=True, nullable=False)
    ciptext = db.Column(db.Text, nullable=False)

    def __repr__(self):
        return f'<Note number: {self.number}'

-

- , Flask-WTF

class TextForm(FlaskForm):
    text = TextAreaField('  ( 1000 )',
                         validators=[DataRequired(), Length(1, 1000)])
    submit = SubmitField('')

• text — . 2 . , . 1000 . .

. .

@app.shell_context_processor
def make_shell_context():
    return {'db': db, 'Note': Note}

,

@app.route('/', methods=['GET', 'POST'])
def index():
    form = TextForm()
    if form.validate_on_submit():
        key = Fernet.generate_key()
        str_key = key.decode('ascii')
        f = Fernet(key)
        bin_string = form.text.data.encode('utf-8')
        cipher_text = f.encrypt(bin_string)
        str_cipher_text = cipher_text.decode('ascii')
        rnumber = random.randint(1000000, 9999999)
        while True:
            n = Note.query.filter_by(number=rnumber).first()
            if n:
                rnumber = random.randint(1000000, 9999999)
                continue
            break
        cipher_note = Note(number=rnumber, ciptext=str_cipher_text)
        link = f'{app.config["SITE_URL"]}/{rnumber}/{str_key}'
        db.session.add(cipher_note)
        db.session.commit()
        return render_template('complete.html', link=link)
    return render_template('index.html', form=form)

, . POST, "". . URL-safe base64, "Ascii" URL. AES-128.

, URL-safe base64, , . , while , , . , html complete.html - . html Flask-Bootstrap, bootstrap.

, . , , . .. .

@app.route('/<rnumber>/<str_key>')
def question(rnumber, str_key):
    link = f'{app.config["SITE_URL"]}/decrypt/{rnumber}/{str_key}'
    return render_template('question.html', link=link)

"" ,

@app.route('/decrypt/<int:rnumber>/<str_key>')
def decrypt(rnumber, str_key):
    cipher_note = Note.query.filter_by(number=rnumber).first_or_404()
    cipher_text = cipher_note.ciptext.encode('ascii')
    key = str_key.encode('ascii')
    try:
        f = Fernet(key)
        text = f.decrypt(cipher_text)
    except (ValueError, InvalidToken):
        return render_template('error.html')
    text = text.decode('utf-8')
    db.session.delete(cipher_note)
    db.session.commit()
    return render_template('decrypt.html', text=text)

. try except.

Heroku

- Heroku. . , 30 , . , .

Heroku Heroku CLI. git
Heroku CLI

$ heroku login

git

$ git init

Heroku. , encnote

heroku apps:create encnote
Creating ⬢ encnote... done
https://encnote.herokuapp.com/ | https://git.heroku.com/encnote.git

, Heroku

heroku addons:add heroku-postgresql:hobby-dev
Creating heroku-postgresql:hobby-dev on ⬢ encnote... free
Database has been created and is available
 ! This database is empty. If upgrading, you can transfer
 ! data from another database with pg:copy
Created postgresql-graceful-12123 as DATABASE_URL
Use heroku addons:docs heroku-postgresql to view documentation

Heroku DATABASE_URL, . , , Flask

nix export FLASK_APP=encnotes.py
Windows set FLASK_APP=encnotes.py

,

$ export DATABASE_URL=sqlite:////home/user/Python/encnote/app.db ( nix )
$ set DATABASE_URL=sqlite:///D:\Python\encnotes\app.db ( Windows )

flask db init
flask db migrate

migrate, . app.db .

.gitignore , git Heroku

venv
__pycache__

- flask , gunicorn. Postgres psycopg2. http https, Flask-SSLify.

requirements.txt

gunicorn
psycopg2

Heroku , Procfile . :

web: flask db upgrade; gunicorn encnotes:app

Heroku. , .

, . SECRET_KEY .

heroku config:set SECRET_KEY=super-secret-work232
heroku config:set FLASK_APP=encnotes.py

DATABASE_URL Heroku,

heroku addons:add heroku-postgresql:hobby-dev

Now we are all set up for deployment. Add our files to git, commit and send to heroku

git add .
git commit -m "Heroku deploy"
git push heroku master

That's it, the application is ready! In this article I showed how easy it is to make small
web applications using the Flask framework and the easy-to-use python module
for cryptography encryption.